If you managed to get to the castle The Lost Castle 2then you've probably met a strange new character named Nia. The game initially introduces her as a girl with amnesia, and after you make significant progress on one of your runs, she'll be brought to your camp.
Contrary to what you might see online, you don't actually have to beat the last boss of the run to meet Nia, but she won't serve you any purpose until you beat the boss. Until then, he'll simply reside in your camp with an unnamed purpose that won't be revealed until he deals with the final boss.
What is Ethereal Nightmare mode and how to unlock it
Ethereal Nightmare Mode is basically the one New Game+ or post-game content The Lost Castle 2. Once you defeat the Demon Sealer Steward and the subsequent boss demon in Black Castleyou will be brought back to camp and successfully complete your first full run. Once back at the camp, head over to Nia who is standing in the middle of the camp near the Ethereal device.
You should get a prompt telling you that Nightmare Mode has been unlocked, and you can also watch a cutscene introducing Nia if she hasn't been hanging around your camp before. Talk to Nia and ask to use the ethereal deviceand you'll be taken to a screen that shows you the various debuffs you can use on your next run and how Ethereal Nightmare will affect your run.
Since the difficulty options in the base game are Easy and Normal, you can think of it as the game's hard mode.
When using debuffs, you'll notice that there are numbers at the top of the bar that fill up when you apply debuffs. These numbers are the depths of the Ethereal Nightmare. You'll need a set number of debuffs to enter each depth, but you'll also need to complete each depth to unlock the next.. So even if you think you're ready to jump to depth 3, you won't be able to do so without clearing 1 and 2 first.
You'll also see a run overview on the right, showing everything you've selected and a breakdown of how it affects you.
This mode is completely designed to test your ability to create a fully fleshed out, cohesive build. The initial run can be beaten with any random combination of items, but the same won't apply to Ethereal Nightmare mode, and you'll need to come up with a functional build strategy to complete it. Doing so will reward you with rare resources and permanent upgrades to your build.
Working on a tank build is strongly recommended, but there are a variety of builds that will work. It will exist achievement for unlocking and completing each depth of Ethereal Nightmare Mode.

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What are the rewards in ethereal nightmare mode
As mentioned, the rewards you get for runs in any Ethereal Nightmare depth, in addition to unlocking related achievements, will be Soul Stones, Soul Flowers, and Champion Relics. These items work as follows:
|
Item |
Description |
|---|---|
|
Soul stones |
Used to improve a weapon's base stats. They work in tandem with Soul Flowers and Champion's Relics, as you must first unlock the weapon's Soul Inscription. If you have a surplus of unused Soulstones, you'll also be able to use Soulstone Smelting to exchange 10 for a chance at a rarer Soulstone, depending on the level of those you're trading with. |
|
Flowers of the soul |
It is used to unlock a specific weapon's soul inscription, which is needed to permanently upgrade it. |
|
Champion's Relics |
Unlocks a random weapon's Soul Inscription without needing Soul Flowers. |
Certainly yes log in with Nia every time you return to camp to make sure she has nothing to offer you herself. Even if you don't plan to adjust the settings for your next run.

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Here's how to beat the Black Forest boss Mad Gardener in Lost Castle 2.